Method of pack rolling ferrous metals



Patented Mar. 17, L936 METHOD OF PACK ROLLING mnmovs METALS Terrence W.Allsworth, Middletown, Ohio, as-

slgnor to The American Rolling Mill Company, Middletown, Ohio, acorporation of Ohio No Drawing. Application November 25, 1933, SerialNo. 699,801

Claims.

I shall describe my invention in connection with, the rolling of ironand steel sheets in packs, and in connection with the preparation ofmetal pieces for pack rolling, in which fields my invention, while it isnot limited thereto, has especial utility.

In the packi'olling of ferrous metals it has been known that for bestresults (a) sheets should have between them a separating substance ofproper characteristics to prevent formation of stickers, i. e. thewelding of the sheets together 1n the pack during the rolling operation,yet, at the same time (b) the sheets should be permitted to adheretogether sufficiently -to form a properly set pack. While the term setpack may have slightly varying meanings under different circumstances,and while it may not necessarily imply that the sheets are so joined, asit were, adhesively one to the other as to produce a. pack which willroll as though it were a unitary piece of metal, yet it does imply, andfor the purposes of this description I intend it to imply, the existenceof ,such a physical relationship between the several sheets which go tomake up the pack, as will permit efiicient pack rolling, and preventflopping as the pack enters the pass of rolls.

It has been known that a proper coating of oxide on the sheets or pieceswouldprevent sticking.

while permitting setting of the pack. In the old Welsh method ofrolling, where the conditions were proper, a suitable coating of oxidecould be produced upon the pieces individually, since sheet bars wereheated and rolled individually, as by being broken down and run over, inthe first stage or part of the rolling operation, and prior to anymatching for pack rolling. Specific problems have, however, arisenprimarily in connection with newer methods of rolling utilizing thenewer raw materials now available for the purpose. I refer to theproducts of the new continuous hot mills which produce strip sheets fromslabs. These mills can furnish as the starting pieces of subsequentrolling operations, sheet or plate material of varying gauges, quite ascheaply as sheet bars per unit weight, but much thinner in gauge and ofmuch greater area. Consequently, there have been developed numerousprocesses of rolling thin bar, rough plate or the like by hand or inautomatic machinery, which processes have the advantage of startingwiththinner raw material and frequently are able to arrive at thinnergauges with fewer heatings or parts. Thus starting with thin bar or thelike, rolling processes have been developed which.call for the initialdoubling of thin bar or pieces, or the formation of packs at the outsetof the rolling operation and prior to the heating operation. As aconsequence, the doubles or packs are heated and rolled priorto theformation upon the surfaces of each individual sheet or'layer, of aproper protective oxide. 5 Secondly, it has been found advisable whenusing such relatively thin materials to remove whatever scale remainsfrom the hot continuous mill operation beforeany subsequent rolling, ifsmooth sheets are to be produced. Hence, the product of the continuoushot mill has been picked prior to subsequent rollings; and it will beobvious that the doubling of pickled pieces, or the formation of pickledpieces into packs before the heating step, is a further factor inpreventing the formation of a proper oxide coating and in producingstickers. Thirdly, the newer methods of rolling have rendered advisablethe use of modern quick furnaces, and particularly furnaces havingneutral or reducing atmospheres which are not conducive to the formationof oxide. Fourthly, where thin material is being used, it is notadvisable to attempt to develop oxide on its surfaces by the oxidationof the material itself and by means of heat unless this can be carefullyregulated and carried on in a very even manner.

Faced with these problems, the art has endeavored to use various inertseparators, but has encountered two primary difliculties: (a) unless theinert separators are applied very evenly, smooth, thin gauge sheets arenot produced; (b) while inert separators if properly used may preventsticking, they appear also to prevent the proper setting of the pack.

- My invention has for its primary object the provision of materials forrolling and a rolling process involvingthe production upon the surfacesof the metal pieces of a protective coating 'which not only acts as aseparator, but also permits setting of the packs. My invention also has49 for its object the provision of an oxide coating upon the. surfacesof sheets or pieces, the-oxide being primarily derived not from the bodymetal of the sheets, but from material superposed thereon in acontrolled manner. My invention also has for its object the provision ofa process of treating metal sheets or pieces to produce coatings thereonof the desired characteristics.

These and other objects of my invention which will be set forthhereinafter or will be apparent 50 to one skilled in the art uponreading these specifications, I accomplish by that certain procedure ofwhich I shall now describe a preferred embodiment of the characteraforesaid.

While I have hereinabove referred to the rolling of the product of themodern continuous hot mill as setting forth a set of circumstances inwhich my invention has especial utility, it will be understood that thisforms no limitation thereon. My

invention has utility under any circumstances in which it is desired toproduce upon the surfaces of metal pieces, coatings of oxide thecharacteristics herein referred to, and quite irrespective of the originof the said metal pieces. My invention is of particular utility inconnection with the treatment of break-downs which may be defined asmaterial suitable for formation into packs and pack rollings, whichmaterial will be uniform enough and of sufficiently light gauge topermit of a finishing rolling operation without any further heating. Itwill be obvious that breakdowns can be formed in a number of ways. Inthe continuous mill as is well known, slabs previously formed by rollingfrom ingots are continuously rolled in a train of tandem hot mills toform rough plate stock, which is then sheared apart into rough plates orbreak-downs. A continuous mill break-down is therefore material whichhas been produced on a continuous mill, which can be formed into packsfor rolling and which will be uniform enough and of suificiently lightgauge to permit of a finishing rolling operation without any furtherheat.

In the practice of my invention I preferably coat my sheets or pieces ina controlled manner with a salt of the body metal which, under theconditions of the subsequent heat treatment, will decompose or beconverted into an oxide. While a number of salts or compounds of ironwill serve the purpose, yet it is important to choose one which (a) iseasily and uniformly applied; (b) may be uniformly converted to theoxide; may be converted to the oxide under modern furnace conditions,and more particularly under neutral or reducing atmospheres; and (d) maybe converted to the oxide under temperatures normally employed forfitting the metal pieces for hot rolling. Under some circumstances it isadvantageous to employ a salt which bears a certain relationship to thepickling operation, where employed. Of the several salts which I mightuse, I prefer to employ ferrous sulphate or copperas. This may, ifdesired, be derived from a pickling bath; but this is not necessary, andit is frequently preferable to apply the ferrous sulphate as anoperation distinct from pickling. Nor is the application of ferroussulphate to already pickled sheets or pieces a necessary limitation uponmy process. I may however, use other salts or compounds such as eitherthe ferric or ferrous nitrate of iron, preferably coating the sheetswith a solution of nitrate of iron containing free acid, but notexceeding one-half of one percent, or chloride of iron, etc.

I prefer to apply the ferrous sulphate or other compound either from asolution or suspension thereof. It is possible to employ a pickling bathcontaining considerable ferrous sulphate either added thereto or derivedfrom the iron pieces in previous pickling operations, and withoutwashing the sheets or pieces after the pickling operation, to permitthem to dry so that they become coated with the ferrous "sulphate. Wherethis is done, however, care must be taken to cause the liquid to dryevenly on the surfaces of the sheets or pieces without collectingunevenly thereon. This maybe done by moving the pieces during the dryingoperation. Moreover, it is preferable not to have too great a quantityof free acid present unless the sheets are to be rolled immediately,

since the free acid would continue its attack upon the iron and producepits.

These considerations render advisable the use of a separate step for theapplication of the salt to the surfaces of the sheets or pieces; and inmy preferred procedure I immerse the pieces in a separate tankcontaining a solution and/or suspension of ferrous sulphate. When thisis separate treatment does not require the maintenance of any relativelylarge content of ferrous sulphate in the pickling tank, but leaves mefree to carry on the pickling itself under optimum conditions. If apickling precedes my coating treatment, it is not necessary to wash orneutralize sheets between the two steps, although this may be done ifdesired.

In the use of a separate coating step I prefer to employ a hot solutionof ferrous sulphate maintained very near the boiling point.concentration of ferrous sulphate may vary considerably, and I haveattained good results using from five to twenty-five per cent by weightof the iron salt. Concentrations between eight and fifteen per cent seemto give optimum results most consistently; but none of the figureshereinabove given appear to be limiting. The acid concentration of theferrous sulphate solution is preferably kept below one per cent byweight although, as I have hereinabove indicated, higher concentrationsof acid may be employed if the pieces are immediately heated forrolling.

In an exemplary procedure in accordance with my invention, the productof the continuous hot mill may be pickled in the usual manner. Then thepieces are dipped into a tank containing the hot ferrous sulphatesolution hereinabove described, and, when withdrawn therefrom, are driedvery rapidly. They will be found to have upon their surfaces a thin,uniform coating of crystallized ferrous sulphate. By pieces I mean, ofcourse, such lengths as may be found suitable for any given rollingoperation. Such lengths may vary from relatively short pieces suitablefor pack formation to strip sheets themselves, or even to continuousbands of metal.

After the coating as aforesaid, packs may be formed of the pieces, thepieces may be doubled, or matched and doubled, or bands of metal may besuperposed to form pack-like structures. These structures are thenpassed to a furnace which may be and preferably will be of the modernquick-acting type having a reducing atmosphere, although this again isnot limiting. When the structures are heated for rolling the ferroussulphate upon their surfaces undergoes a change of state, which Ibelieve comprises first, a loss of the water of hydration, and second,as the heat in the structure increases, a decomposition to form ferricoxide and the oxides of sulphur, which latter materials, of course, passoff in the form of gas. In the presence of reducing atmospheres in theheating furnaces, the ferric oxide is partly reduced to ferrous oxide inmost cases, the mixture of ferric and ferrous oxides (ordinarily termedmagnetic oxide) forming a thin uniform coating over the surfaces of thepieces. Under The differing conditions the various oxides appear to besomewhat differently formed, and I do not desire my invention to belimited to any particular oxides or mixture of oxides, nor to any theoryof the nature of the decomposition which takes place. A thin uniformcoating of oxide permits the pack to set uniformly and solidly betweenthe rolls of the mill, after which the pack can be elongated to thedesired length. Uniformity of coating as hereinabove set forth is ofgreat importance, since the packs may have a tendency to roll apart orbreak open in areas having had too heavy a coating, or in the case ofadjacent areas having no coating to weld together forming stickers.

Having thus described my invention, what I claim as new and desire tosecure by Letters Patent, is:

1. A process of preparing ferrous metal breakdowns for pack rolling,which comprises the steps of dipping said metal pieces into a liquidcontaining a compound of the metal of said pieces adapted to beconverted into an oxide of said metal, drying said pieces so as to forma uniform coating of said compound upon the surfaces thereof, andconverting said compound into an oxide.

2. A process of preparing ferrous metal pieces for hot rolling whichcomprises dipping said pieces into a liquid containing ferrous sulphate,said liquid being maintained at a temperature high enough to promoterapid drying of said pieces when removed therefrom, removing and dryingsaid pieces, forming said pieces into plural layered units for rolling,heating said units, and rolling said units.

3. A process of preparing ferrous metal pieces for hot rolling whichcomprises dipping said pieces into a liquid containing ferrous sulphate,said liquid being maintained at a temperature high enough to promoterapid drying of said pieces when removed therefrom, removing and dryingsaid pieces, forming said pieces into plural layered units for rolling,heating said units rapidly under non-oxidizing conditions, and rollingsaid units.

4. A process of preparing ferrous metal pieces for pack rolling whichcomprises dipping said metal pieces into a solution containing betweenfive to twenty-five per cent by weight of ferrous sulphate, saidsolution being maintained near the boiling point thereof, withdrawingsaid pieces and rapidly drying them so as to form upon their surfaces acoating of ferrous sulphate, and subsequently converting said ferroussulphate to the oxide form under the influence of heat.

5. A process of preparing ferrous metal pieces for hot rolling whichcomprises coating said pieces with a liquid containing ferrous sulphate,said liquid being maintained at a temperature high enough to promoterapid drying of said pieces in air, drying said pieces, forming saidpieces into plural layered units forrolling, heat ing said units, androlling said units.

TERRENCE W. ALISWOR-TH.

